The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.
Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic or photolithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate.
The numerous processing steps outlined above are used to cumulatively apply multiple electrically conductive and insulative layers on the wafer and pattern the layers to form the circuits. Circuit elements include metal lines which connect various components with each other in a horizontal plane, as well as contact vias, which extend through insulative layers and provide electrical conduction between vertically-spaced conductive layers or circuit components. The final yield of functional circuits on the wafer depends on proper application of each layer during the process steps. Proper application of those layers depends, in turn, on coating the material in a uniform spread over the surface of the wafer in an economical and efficient manner.
Throughout the IC fabrication process, the WIP wafers must be frequently tested to monitor the physical and electrical properties of the devices being fabricated thereon. Wafer testing is carried out on sample wafers using a measurement tool and equipment to analyze the data. These testing tools and equipment may use physical methods that allow ions, electrons and/or electromagnetic radiation to interact with the device features, and then examine the secondary particles and/or radiations that are produced. The information obtained from the interaction of the particles and/or radiation with a region of interest in the device is then used to deduce the properties of the materials in the region of interest. The information may reveal the presence of defects, which are characteristics of the wafer or results of the wafer fabrication process that cause nonconformance to the specified wafer requirements.
In the manufacture of semiconductor devices, failure analysis and characterization of circuits frequently requires that waveform measurements be obtained from circuit elements. During the integrated circuit development phase, the device is subjected to various test conditions such as speed, temperature, etc. Performance parameters of the device are obtained by acquiring waveforms from key circuit nodes such as clock lines, enable signals, address buses and data buses, in the device. If the performance parameters indicate the presence of defects in the device, it is necessary to trace back the source of the defects in order to take corrective measures.
Waveform data can be acquired from circuit elements by direct-contact mechanical probing or electron beam probing. This is accomplished by establishing electrical contact between a testing apparatus and one or more of the numerous input/output (I/O) circuit elements in the device. In some instances, these I/O circuit elements are placed in the periphery of the device or located in such a manner as to provide some degree of access to the active surface of the device by some form of mechanical or electron beam probe during operation.
Conventional methods of probing circuit elements for failure analysis of a device include initially sputtering a probing pad on a metal line or other element in the circuit in order to enlarge the contact area for the metal test probe of a testing apparatus. The test probe of the testing apparatus is then placed into contact with the probing pad to test various electrical characteristics of the circuit through the pad. However, one of the limitations of using the probing pad is that the probing pad introduces a relatively high contact resistance into the electrical conduction between the metal line or other element and the test probe. This may result in attenuated electrical signals that are picked up by the test probe and translate into faulty test data obtained from the device. Furthermore, because metal lines of a device typically run in closely-spaced, adjacent relationship to each other, the contact pads often establish electrical contact between two or more adjacent metal lines in the circuit. This causes electrical bridging and leakage which, in turn, results in faulty test data. In the case of circuit elements which are relatively isolated electrically from adjacent elements in the device, the test probe may be placed directly into contact with the metal line or other element in order to reduce the high contact resistance imparted by the probing pad as well as electrical bridging or junction leakage between circuit elements that may be otherwise caused by using a probing pad. However, such direct contact between the test probe and the circuit element can be used only under limited circumstances, since direct probing of metal lines or other elements in a dense circuit layout would cause simultaneous electrical contact of the test probe with one or more adjacent metal lines or elements in addition to the line or element being tested. Accordingly, a new and improved method is needed for probing elements of an integrated circuit device and which method avoids the contact resistance and other drawbacks of providing electrical contact between a test probe and an element in the circuit through a probing pad.
An object of the present invention is to provide a new and improved method of probing elements of an integrated circuit (IC) device for the purpose of electrical testing or measurement.
Another object of the present invention is to provide a new and improved IC device circuit probing method which can be used to probe a variety of IC circuit elements.
Still another object of the present invention is to provide a new and improved method of probing various circuit elements in an IC device, which method includes providing a probe access trench adjacent to a circuit element and providing electrical contact between a test probe and the element through the trench.
Yet another object of the present invention is to provide a new and improved probing method for the electrical testing and/or measurement of an IC device, which probing method includes providing a probe access trench in a substrate adjacent to the circuit element to be tested; providing a liner pad over the trench; and providing electrical contact between a test probe and the circuit element through the trench.
A still further object of the present invention is to provide a new and improved probing method which may be used for the electrical testing and/or measurement of metal lines, contact vias or p/n junctions in an IC device.